6.3 Neurosecretory Role of Hypothalamus

The hypothalamus is part of the forebrain and serves as the master control centre of the endocrine system. It contains special groups of neurosecretory cells that produce regulatory hormones, which control the synthesis and secretion of pituitary hormones. The hypothalamus also produces two primary hormones, ADH and oxytocin, which are stored in the posterior pituitary gland.

Definition

Neurosecretory Role of Hypothalamus: The hypothalamus contains special groups of neurosecretory cells that conduct impulses and have developed secretory capacity to a high level. These cells produce regulatory hormones which regulate the synthesis and secretion of pituitary hormones.

Neurosecretory Cells: Neurosecretory cells are specialized neurons that conduct impulses and have developed secretory capacity to a high level. They produce regulatory hormones.

Main Idea

• Hypothalamus is part of the forebrain.
• It regulates a wide spectrum of physiological functions.
• It monitors metabolites and hormone levels in the blood.
• It is the master control centre of the endocrine system.
• Its endocrine signals directly control the pituitary gland.
• It contains special groups of neurosecretory cells.
• These cells produce regulatory hormones.
• Regulatory hormones regulate the synthesis and secretion of pituitary hormones.
• The hormones produced by the hypothalamus are either releasing factors or inhibiting factors.
• These are produced in the cell bodies, packed into granules, and transported down the axon by cytoplasmic streaming.
• The axon endings synapse with blood capillaries and release hormones into the blood.
• The hypothalamus also produces ADH and oxytocin, which are stored in the posterior pituitary.

Core Concept

• Hypothalamus = part of forebrain
• Functions = regulates hunger, thirst, sleep, temperature
• Monitors = metabolites and hormone levels
• Master control centre = of endocrine system
• Neurosecretory cells = conduct impulses; secrete hormones
• Regulatory hormones = releasing factors and inhibiting factors
• Releasing factors = stimulate pituitary hormone secretion
• Inhibiting factors = inhibit pituitary hormone secretion
• Transport = produced in cell bodies; packed into granules; transported down axon
• Release = axon endings synapse with blood capillaries
• ADH and oxytocin = produced by hypothalamus; stored in posterior pituitary

Detailed Explanation

Neurosecretory Role of Hypothalamus

• Hypothalamus is part of forebrain.
• It regulates a wide spectrum of physiological functions such as hunger, thirst, sleep and temperature.
• Hypothalamus also monitors metabolites and hormone levels in the blood.
• The hypothalamus is the master control centre of the endocrine system.
• Its endocrine signals directly control the pituitary gland.
• It contains special groups of neurosecretory cells.
• These cells conduct impulses and have developed secretory capacity to a high level.
• These cells produce regulatory hormones which regulate the synthesis and secretion of pituitary hormones.
• The hormones produced by the hypothalamus are either the releasing factors which stimulate secretions of pituitary hormones or inhibiting factors which inhibit secretion of pituitary hormones.
• These are produced in the cell bodies of the cells and packed into the granules and are transported down to the axon by cytoplasmic streaming.
• The axon endings of the neurosecretory cells synapse with blood capillaries and release their hormones into the blood when stimulated, which carry them to target area.
• The hormones from hypothalamus and their functions are given in the given table.
• In addition, the neurosecretory cells that arise from the hypothalamus also produce two primary hormones i.e., antidiuretic hormone (ADH) and oxytocin which are stored in posterior lobe of pituitary gland and are released from here when needed.

Table of Hypothalamic Hormones and Their Effect on Pituitary Gland

Summary Table of Hypothalamic Hormones

Intermediate Level

Neurosecretory Role of Hypothalamus

Regulatory Hormones

Transport and Release of Hypothalamic Hormones

ADH and Oxytocin

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Hypothalamus is part of the forebrain.
• 2. It regulates hunger, thirst, sleep, and temperature.
• 3. It monitors metabolites and hormone levels.
• 4. It is the master control centre of the endocrine system.
• 5. Its endocrine signals directly control the pituitary gland.
• 6. It contains neurosecretory cells.
• 7. Neurosecretory cells conduct impulses and secrete hormones.
• 8. They produce regulatory hormones.
• 9. Regulatory hormones regulate pituitary hormone secretion.
• 10. Releasing factors stimulate pituitary hormone secretion.
• 11. Inhibiting factors inhibit pituitary hormone secretion.
• 12. Hormones are produced in cell bodies.
• 13. Hormones are packed into granules.
• 14. Hormones are transported down the axon by cytoplasmic streaming.
• 15. Axon endings synapse with blood capillaries.
• 16. Hormones are released into the blood.
• 17. GHRF stimulates GH secretion.
• 18. Somatostatin inhibits GH secretion.
• 19. TRF stimulates TSH secretion.
• 20. CRF stimulates ACTH secretion.
• 21. PIF inhibits prolactin secretion.
• 22. GnRH stimulates FSH and LH secretion.
• 23. ADH and oxytocin are produced by the hypothalamus.
• 24. ADH and oxytocin are stored in the posterior pituitary.

Remember

• - Hypothalamus = part of forebrain
• - Functions = regulates hunger, thirst, sleep, temperature
• - Monitors = metabolites and hormone levels
• - Master control centre = of endocrine system
• - Neurosecretory cells = conduct impulses; secrete hormones
• - Regulatory hormones = releasing factors and inhibiting factors
• - Releasing factors = stimulate pituitary hormone secretion
• - Inhibiting factors = inhibit pituitary hormone secretion
• - **GHRF** = stimulates GH
• - **Somatostatin** = inhibits GH
• - **TRF** = stimulates TSH
• - **CRF** = stimulates ACTH
• - **PIF** = inhibits prolactin
• - **GnRH** = stimulates FSH and LH
• - ADH and oxytocin = produced by hypothalamus; stored in posterior pituitary

Common Mistakes

• 1. Confusing releasing and inhibiting factors — Releasing factors stimulate; inhibiting factors inhibit.
• 2. Mixing up the hypothalamic hormones — GHRF, somatostatin, TRF, CRF, PIF, GnRH.
• 3. Forgetting the role of the hypothalamus — Master control centre of the endocrine system.
• 4. Thinking the hypothalamus only controls the pituitary — It also regulates hunger, thirst, sleep, and temperature.
• 5. Confusing ADH and oxytocin — ADH = water retention; oxytocin = childbirth and milk ejection.
• 6. Forgetting the storage site of ADH and oxytocin — Posterior pituitary.
• 7. Mixing up the effects — GHRF stimulates GH; somatostatin inhibits GH.
• 8. Believing the hypothalamus is not part of the brain — It is part of the forebrain.
• 9. Thinking the hypothalamus produces only releasing factors — It also produces inhibiting factors.
• 10. Mixing up the target of hypothalamic hormones — They target the pituitary gland.

Quick Revision

Hypothalamus is part of forebrain. It regulates a wide spectrum of physiological functions such as hunger, thirst, sleep and temperature. Hypothalamus also monitors metabolites and hormone levels in the blood. The hypothalamus is the master control centre of the endocrine system. Its endocrine signals directly control the pituitary gland. It contains special groups of neurosecretory cells. These cells conduct impulses and have developed secretory capacity to a high level. These cells produce regulatory hormones which regulate the synthesis and secretion of pituitary hormones. The hormones produced by the hypothalamus are either the releasing factors which stimulate secretions of pituitary hormones or inhibiting factors which inhibit secretion of pituitary hormones. These are produced in the cell bodies of the cells and packed into the granules and are transported down to the axon by cytoplasmic streaming. The axon endings of the neurosecretory cells synapse with blood capillaries and release their hormones into the blood when stimulated, which carry them to target area. In addition, the neurosecretory cells that arise from the hypothalamus also produce two primary hormones i.e., antidiuretic hormone (ADH) and oxytocin which are stored in posterior lobe of pituitary gland and are released from here when needed.

60-Second Revision

• Hypothalamus = part of forebrain
• Functions = regulates hunger, thirst, sleep, temperature
• Monitors = metabolites and hormone levels
• Master control centre = of endocrine system
• Neurosecretory cells = conduct impulses; secrete hormones
• Regulatory hormones = releasing factors and inhibiting factors
• Releasing factors = stimulate pituitary hormone secretion
• Inhibiting factors = inhibit pituitary hormone secretion
• GHRF = stimulates GH
• Somatostatin = inhibits GH
• TRF = stimulates TSH
• CRF = stimulates ACTH
• PIF = inhibits prolactin
• GnRH = stimulates FSH and LH
• ADH and oxytocin = produced by hypothalamus; stored in posterior pituitary
• Warning: Hypothalamus is the master control centre of the endocrine system

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• 6. Endocrine System of Man

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• 6.4 FEEDBACK MECHANISM

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